The bearing surfaces in internal combustion engines are subjected to relatively high loads because of the compression pressures necessary to effect combustion in these devices. The life expectancy of internal combustion engines has been found to depend significantly upon the high-wear status of the bearings under conditions of high loads and minimal lubrication found during startup. This dependency is often the cause for more frequent and expensive overhaul work to keep the engine in operation. During such overhauls, it has been regularly observed that the crankshaft bearings are exhausted long before expected, even though they were properly installed and the oil supply system was operating as designed.
A variety of approaches have been previously attempted to alleviate this problem, one such approach being exemplified by U.S. Pat. Nos. 3,583,525; 3,583,527; 3,722,623; 3,917,027; 4,061,204; 4,094,293; 4,112,910; 4,157,744; and 4,199,950. These patents generally teach that the problem relates to a lack of lubrication at start-up, and disclose systems having variously configured auxiliary oil accumulators which through appropriate valving bleed off and store a portion of the oil supply during normal engine operation and release it to the engine using pressurized air prior to or at the time of the next restart. Typically this pressuring gas is either not isolated from the oil supply or is isolated using ineffective and/or inefficient mechanisms such as pistons or partition membranes. Those accumulator-based approaches using air are limited by the large volumes of oil required to achieve normal operating oil pressures for the initiation of combustion, especially in the case of very large internal combustion engines which often require the pumping of up to five gallons of oil before normal operating oil pressures are attained. Because space is already at a premium in these very large engine compartments, it is often not desirable to include an auxiliary oil accumulator having a such a large volume. Further, the use of large volume pressurized air pre-oilers would tend to create large variations in the rate of and/or pressure of the oil supplied to the engine since the air pressure within the tank will decrease with increasing air volume.
Another approach is exemplified by U.S. Pat. Nos. 4,058,981 and 4,126,997, which disclose that inadequate start-up lubrication is the cause of the problem and teach a valve system which initially routes engine oil to more critical engine components such as the turbocharger and crankshaft bearings upon start-up, and thereafter to less critical engine components. This approach is beneficial, but since it does not become operative until engine parts begin relative movement, but premature wear of less-critical engine elements is still a problem.
Another approach, exemplified by U.S. Pat. No. 3,045,420, involves the use of a plurality of oil pumps, each supplying oil to separate engine lubrication systems. The pump, which supplies oil to the turbocharger unit of the engine, is actuated prior to combustion, continues to operate during engine operation, and operates for a brief period after engine shutdown to protect the relatively sensitive high speed turbocharger bearings. This system may be beneficial in extending the turbocharger life expectancy, but it does not protect other vital engine components, it introduces substantial complexity into the lubrication system of the engine, and failure of the turbocharger pump would lead to turbocharger failure within seconds.
In still another approach as exemplified in U.S. Pat. No. 4,502,431, oil is pumped within the engine passageways prior to cranking for a period sufficient to provide an operational oil pressure level before any engine parts begin to move. In this manner, all bearing surfaces are fully lubricated in advance of their load-bearing operation and life expectancy is substantially increased. This result is accomplished by providing a supplemental oil pump which is driven from the starter motor armature shaft of the diesel engine. When the starter switch of the internal combustion engine is engaged, an electrical impulse is first provided to initiate the rotation of the starter motor armature shaft to drive the supplemental oil pump, thereby bringing oil pressure up to operational levels before the initiation of actual engine cranking. When the starter motor is actuated to turn the crankshaft to initiate combustion, both the main and supplemental oil pumps become operative. As the starter motor automatically disengages and is de-energized upon combustion, the supplemental oil pump stops. A main oil pump that is smaller and less expensive than normally utilized is sufficient to maintain the already-established oil pressure.
Finally, manufacturers of internal combustion engines are known to attempt to minimize the problem of premature engine component wear by incorporating relatively large capacity oil pumps in the lubricating system in order to minimize the period between initial combustion and when engine oil pressure reaches its normal operating level. These latter approaches have not had the desired result of optimally reducing wear, and they have caused the undesirable effects of introducing unnecessary weight, size, complexity and expense to the engine and auxiliary assemblies.
It has been found that the extensive and premature wear of internal combustion engines is due to factors which include inadequate start-up lubrication. The problem of premature wear has been correlated to the time the engine is not used, the lubricity of the oil and the tenacity of its adhesion to bearing surfaces. In the conventional internal combustion engines, the oil pump mechanism is driven by gears from the crankshaft. Thus, oil is not directly provided to engine parts until after such parts have begun moving. Depending upon the size of the engine and the capacity of the pumping mechanism, normal operating oil pressure is normally not obtained in the system for five or more seconds after cranking begins. Only residual oil remaining on the bearing surfaces from the previous operation provides lubrication and protection until a new supply of oil is provided by the pump. Newer high lubricity oils increase the fuel economy of the engine, but they also tend to promote start-up wear when engines are not operated for periods of time. Such oils tend to lack adhesion tenacity and leave minimal residual oil on bearing surfaces when an engine is not in use, resulting in bearings being left relatively unlubricated during the initial start-up period. The present invention provides a relatively simple and effective mechanism to extend the life of the bearing surfaces of an internal combustion engine, by assuring that an adequate oil supply is provided to the bearing surfaces before any relative movement of engine parts occurs.
The present invention solves the above problems by providing a captive bag in an accumulator tank to accumulate and release oil for engine lubrication prior to combustion. The bag is filled with air or an easily condensible gas which undergoes compression as the oil is accumulated in the accumulator tank to provide the pressure source for forcing the oil into the engine to initiate the pre-combustion lubrication process. Because of the use of a captive bag, the oil is kept isolated from the air or condensible gas allowing the accumulator tank to be placed in any position rather that upright as is necessary to prevent air loss with accumulators not having a oil isolation mechanism. Further, the captive bag technique prevents any absorption or chemical interaction between the oil and the gas, and also minimizes or eliminates air leakage which would ultimately incapacitate the accumulator function. Finally, the captive air bag is easier to replace than conventional membranes which could be used to accomplish the same function.
Because of the use of a condensible gas undergoing a phase change in the preferred embodiment, the overall size of the accumulator is minimized to only that volume of oil needed for pre-oiling plus a minor volume for the bag material and the condensed liquid, thus substantially reducing the overall volume of the tank necessary for subsequent pre-ignition oiling. Further the use of a condensible gas rather than air allows the oil pressure delivered by the pre-ignition oiler to be relatively constant since it will be determined by the essentially constant vapor pressure of the gas at pre-oiling temperatures rather than the wide variations in air pressure which would be encountered with the use of accumulators utilizing air as oil is released from the tank.
Accordingly, it is an object of the present invention to provide an apparatus to accumulate and release oil for engine lubrication prior to combustion.
It is another object of the present invention to provide an apparatus to accumulate and release oil for engine lubrication prior to combustion which is filled with air or an easily condensible gas which undergoes compression as the engine lubricating material is accumulated in the accumulator tank to thereby provide the pressure source for forcing the engine lubricating material into the engine to initiate the pre-combustion lubrication process.
It is another object of the present invention to provide a captive bag in an accumulator tank to accumulate and release oil for engine lubrication prior to combustion which minimizes air leakage and prevents any absorption or chemical interaction between the engine lubricating material and the pressure source material.
It is another object of the present invention to provide an apparatus to accumulate and release oil for engine lubrication prior to combustion which utilizes a condensible gas which undergoes a phase change from a gaseous state to a liquified state as the engine lubricating material is accumulated and which undergoes a phase change from a liquified state to a gaseous state as the engine lubricating material is released into the engine.
It is another object of the present invention to provide an apparatus to accumulate and release oil for engine lubrication prior to combustion which utilizes a condensible gas that provides a substantially constant pressure to deliver the engine lubricating material to the engine.
It is another object of the present invention to provide a captive bag in an accumulator tank to accumulate and release oil for engine lubrication prior to combustion which substantially reduces the overall volume of the accumulator necessary for use in pre-combustion engine lubrication.
It is another object of the present invention to provide a captive bag to accumulate and release oil for engine lubrication prior to combustion which improves the ease of maintenance and repair of the engine lubrication system.
It is another object of the present invention to provide a means of enhancing the volume of oil delivered by the accumulator.